At present, apparatuses for cutting pipes are largely classified into a mechanical cutting apparatus and a fusion cutting apparatus. The mechanical cutting apparatus includes a high-speed cutting machine using a cutting grindstone, a sawing machine using a saw blade, and the like, and the fusion cutting apparatus includes an oxygen cutting machine and a plasma cutting machine.
The mechanical cutting apparatus is an apparatus having a size equal to or greater than a diameter of a pipe to be cut for cutting thereof, and is used to cut small tubes. The fusion cutting apparatus is used to cut large tubes.
The cutting apparatus require considerable time and cost in piping and welding work since it is difficult to vertically cut the tubes and it is impossible to bevel the tubes. For this reason, this is a major cause of fire together with poor work environments.
The cutting apparatus generates lots of noise and dust during cutting or grinding for bevels, and the generated fine dust includes a stone powder as raw material of the cutting grindstone, an adhesive, and a powder of the cut basic material. The fine dust generated during cutting/grinding deteriorates work environments and is fixed to the pipes to thereby aggravate contamination of drinking water and have a fatal influence on production equipment.
In particular, since cleanliness of production structures and purity of pipes are core factors to production in high-tech industries such as semiconductor/electronic/LCD industries, cutting apparatuses using carbide blades are expensively imported and used to maintain the purity of the pipes. However, the expensive cutting apparatuses are not enlarged and supplied to general construction pipe equipment. In addition, considerable time and cost are consumed since special methods of cutting and beveling pipe materials and nonferrous metal (copper, stainless steel, etc.) having large magnitude and plastic lining pipe materials are not present.
Cutting methods and problems according to types of cutters are indicated by the following Table 1.
TABLE 1Types and problems of cuttersCutter TypeCutting MethodProblemsHigh-speedGrinding of cutting1) A large amount of dust (stone, adhesive,Cutting Machinestoneiron powder, etc.) is generated: harmfulsubstances are inserted into pipes.2) There is a lot of noise and poorenvironments are created due to external dust.3) A large number of sparks are generated:there is a risk of fire or burns.4) Burrs are generated: a load is generated influid flow and scale and blockage are caused.5) A method of grinding a cutting stone byvertical displacement:It is impossible to cut tubes having largediameters (limit of the cutting stone); andIt is impossible to cut vertically precise tubes.Sawing MachineUse of band type saw1) A method of using a band type saw blade bybladevertical displacement:It is impossible to cut tubes having largediameters (limit of the band type saw bladeand the machine);It is impossible to cut vertically precisetubes; andA cutting time is long (poor profitability).2) Durability is decreased due to use of a high-speed steel blade instead of a carbide blade:Cutting oil is used (environment and waterpollution).Oxygen/PlasmaFusion cutting1) Corrosion is accelerated due to oxidation byCutting Machinecutting heat (a non-welding joint beingunavailable).2) Foreign substances are fixed into pipes anda risk of fire is increased by sparks.3) A countermeasure for preservation andmanagement of flammable gas is required (riskof explosion accident).4) It is impossible to cut copper tubes/stainlesstubes/clad steel tubes/lining steeltubes/synthetic resin tubes.5) A poor cut surface is generated (grinding forsurface treatment).
To resolve these problems, an economic and efficient processing machine for only pipes (cutting, beveling, and welding) has been devised to achieve improvement in environment/safety of a work space, cost reduction, improvement in welding quality, quality improvement of drinking water, equipment protection of industry field, and profitability improvement. Accordingly, a mechanical cutting machine using a carbide blade has been used about 15 years ago and technical development thereof is performed in the foreign country, and a mechanical cutting machine using a carbide blade has been developed about 5 years ago in the domestic country. For example, this is disclosed in Korean Patent Laid-open Publication No. 2009-0101426 (Sep. 28, 2009) (Hereinafter, referred to as “prior art 1”), Korean Patent Publication No. 1077252 (Oct. 27, 2011) (Hereinafter, referred to as “prior art 2”), and Korean Patent Laid-open Publication No. 2012-0040524 (Apr. 27, 2012) (Hereinafter, referred to as “prior art 3”), which are incorporated by reference.
As a representative example of the mechanical cutting machine using a carbide blade, there is a cutting/beveling machine developed 10 years ago for simultaneously performing cutting and beveling, similar to that of the prior art 1, as illustrated in FIGS. 1 and 2.
The prior art will be described below with reference to FIGS. 1 and 2. In the prior art, a main body 10 is provided such that a tube material p is positioned and fixed at a center thereof. A drive wheel 20 rotated by an electric motor 15 is coupled to one side (front side) of the main body 10 while the tube material p penetrates the drive wheel 20. A cutting tool 31 and a beveling tool 32 are mounted in front of the drive wheel 20 so as to face each other (or two or more tools are balanced and provided in front of the drive wheel 20), and the cutting tool 31 and the beveling tool 32 vertically move (in a center direction of the tube material) by a predetermined length whenever the drive wheel 20 rotates once. In this case, the cutting tool 31 and the beveling tool 32 are mounted to a block 40 for guide such that the cutting tool 31 and the beveling tool 32 reciprocate in the center direction of the tube material p in front of the drive wheel 20. The block 40 is screwed to a rotary shaft 50 again and the rotary shaft 50 has a gear 51 formed at an upper end thereof. Accordingly, the rotary shaft 50 vertically moves the block 40 by a pitch of an angle of rotation of the gear 51 whenever the gear 51 comes into contact with a latch 60 protruding from the main body 10, and thus the cutting tool 31 and the beveling tool 32 mounted to the block 40 enter in the center direction of the tube material p.
The apparatus according to the prior art is an apparatus which cuts or simultaneously bevels the tube material while penetrating the same by a predetermined depth whenever the cutting tool 31 and the beveling tool 32 rotate about the tube material p once. However, the apparatus of the prior art has a slow processing speed. That is, since the gear 51 and the rotary shaft 50 are coupled to the block 40 in a simple screw manner, there is a problem in that, when the rotation speed of the drive wheel 20 is increased in order to increase the processing speed, the rotary shaft 50 rotates over a desired angle by strong striking between the gear 51 and the latch 60, thereby exceeding a proper processing depth. In addition, when the gear rotates by one pitch, the gear is smoothly caught by the latch during next rotation thereof. However, when the gear strongly strikes the latch by inertia during rotation at high speed, the gear rotates by 1.5 pitches instead of one pitch. For this reason, when the gear rotates next, the gear is not caught by the latch but passes the latch. In addition, the drive wheel 20 should be rotated in a reverse direction for a long time in order to return the cutting tool 31 and the beveling tool 32 to an original position after cutting the tube material p, or the gear 51 should be returned to an original position by manual reverse rotation after the latch 60 is lifted upward such that the gear 51 is not engaged with the latch 60.
In order to resolve the problems of the above prior art, a pipe cutting apparatus according to the prior art 2 is devised.
In the prior art 2, a rotary shaft is coupled into a gear in a latch form and reaction force of a spring is applied thereto, so that the rotary shaft rotates only by a uniform angle. A return means for reverse rotation of the rotary shaft by selectively tightening a head portion of the rotary shaft is further provided at an upper side of the rotary shaft.
The prior art 2 helps to resolve the above problems of the prior art 1. However, the prior art 2 does not resolve stubborn problems of the prior art 1, such as a problem in which processing to various shapes is not performed, a problem in which a thick tube material having a certain or more thickness is not cut, a problem of damage due to an impact between a gear and a latch, a problem in which a cutting depth is not adjusted, and a problem in which a beveling blade is frequently replaced according to a bevel angle and a bevel shape.
The above problems will be described in more detail. In the prior arts 1 and 2, the tube material is processed in order illustrated in FIG. 3. That is, the cutting tool 31 and the beveling tool 32 process the tube material p in second to fourth orders while entering the tube material p as illustrated in the first drawing of FIG. 3 and then gradually deeply entering the same, thereby allowing cutting and beveling to be performed together. Accordingly, the prior arts 1 and 2 have a limit in that only the processing such as cutting processing illustrated in FIG. 4(a), cutting and one surface beveling processing illustrated in FIG. 4(b), and cutting and both surfaces beveling processing illustrated in FIG. 4(c) is performed on the tube material.
As illustrated in FIG. 5, the cutting tool 31 should naturally have a longer length than a thickness t of the tube material to be cut, for cutting the tube material. However, when the cutting tool has an increased length L to cut the tube material having a thickness t of several tens mm or more, the cutting tool is easily damaged without enduring force applied thereto during cutting.
In addition, as illustrated in FIG. 6, the beveling tool 32 for performing improved processing on a cut surface of the tube material should naturally have a longer blade length 1b than an inclined surface of the tube material to be cut. However, since the beveling blade length 1b is longer than a cutting blade length 1c as illustrated in FIG. 7, the beveling blade has to endure a load corresponding to the force applied thereto.
In addition, the prior arts 1 and 2 relate to a method of cutting the center portion of the tube material by a predetermined depth value when the cutting tool rotates once. It is understood that a load applied during cutting and a load applied during beveling, namely, different transverse cutting forces P act on the material. Here, the transverse cutting force P is determined by a specific cutting resistance Ks, a cutting width l, and a processed depth dp according to a material to be cut, and is indicated by Equation as follows.P=Ks×l×dp 
Accordingly, as illustrated in FIG. 7(b), a pitch is calculated since the cutting width lc and the processed depth dp are predicted without regard to the specific cutting resistance according to the material to be cut when a cutting tip for cutting is used. On the other hand, as illustrated in FIG. 7(a), it is difficult to calculate a proper pitch value (a processed depth value per one rotation) for beveling processing since the cutting width l is changed according to the thickness t of the tube material in the beveling work. For this reason, it is difficult to commercialize the apparatus since the prior arts do not satisfy various work requirements, and the beveling tool is often damaged or there is a problem in tool design to overcome the same.
In addition, the cutting tool and the beveling tool cut the material to a predetermined depth by dropping whenever the gear is caught by the latch and rotates by a certain angle. When the cutting tool and the beveling tool cut and bevel the tube material having a thickness of several tens mm or more, the gear, components located therebelow, and the latch may be damaged by several hundreds of impacts between the gear and the latch. For example, when it is assumed that the gear has five protrusions, a pitch of 1 mm is a case in which the gear rotates once, and the tube thickness is 20 mm, the latch strikes the gear five times to cut the tube material of 1 mm and the latch strikes the gear 100 times to cut the tube material of 20 mm. 10,000 impacts are generated when such an operation is performed 100 times a day, and 1,000,000 impacts are generated when the operation is performed for 100 days. Such an impact causes a larger impulse when the gear rotates at high speed, and has a bad influence on durability of the apparatus.
Since the cutting is performed by a predetermined depth only when the gear is caught by the latch in the prior arts 1 and 2, a selection range of a workpiece in which the cutting depth is not arbitrarily adjusted is decreased. That is, the cutting speed, the cutting depth, and the like of the workpiece are determined according to materials and types of used tools, but there is a problem in that such processing conditions are not adjusted even though the processing conditions are present in the prior arts 1 and 2.
In addition, the bevel angle of the tube material may vary according to types and designs of tube materials. However, the prior arts 1 and 2 have inconvenience in that the beveling tool is necessarily replaced to change the bevel angle.
Meanwhile, the prior art 3 relates to an apparatus for processing ends of pipes. The prior art 3 relates to a technique of cutting an outer diameter and an inner diameter of a tube material and processing various complicated shapes in such a manner that a main body to which a processing body as a cutting tool is mounted enters toward an end surface of the tube material or adjustably moves in a center direction or an outward direction of the tube material.
However, the prior art 3 is utilized to improve a cut surface of the tube material after a cutting process is completed. Therefore, the prior art 3 has a problem in that productivity is decreased and a cutting process is previously performed using a separate cutting machine, compared to the prior arts 1 and 2 in which the cutting and beveling of the tube material are simultaneously performed. When a pipeline operation is performed in a marine or shipbuilding plant and a petrochemical plant, an improvement operation is essential to weld pipes. In this case, when the tube material having a large diameter range and a large thickness range is processed using the cutting/beveling apparatus of the prior art 3, it is inconvenient and inefficient in that the tube material having a weight of several hundred Kg or more is cut by a cutter and is then lifted and put on the apparatus of the prior art 3 so as to perform the improvement operation. In addition, since the improvement operation is performed on both ends of the pipe, it is inconvenient and inefficient in that the heavy pipe is reversely turned for the improvement operation of an opposite end and then the improvement operation is performed on the opposite end.